The present invention generally relates to photolithography processes used to make semiconductor devices, and more specifically relates to a method of photolithography where a coupling layer is employed between the photo resist and an anti-reflective coating or layer, thereby improving the resolution of the resulting resist image.
Presently, deep ultra violet (DUV) (i.e., 365 nanometers (nm), 248 nm, 193 nm and 157 nm) exposure systems are being used for the production of advanced semiconductor devices. Such a system typically provides as shown in FIG. 1, wherein a thin film 10 to be imaged is deposited on a wafer 12, and a photo resist 14 is laid down above the substrate 10. As shown in FIG. 1, due to the high reflectivity of semiconductor substrates at these wavelengths, typically an anti-reflective coating (ARC) 16 must be provided between the substrate 10 and the photo resist 14. The anti-reflective coating 16 works to keep the deep ultra violet energy 18 from reflecting back into the photo resist 14, thereby improving photo resist process performance and maintain critical dimensions control at, for example, sub-0.250 micron features sizes and smaller.
Typically, the attenuation ability of an anti-reflective coating is changed by adjusting the chemicals which are used to generate the anti-reflective coating 10 and/or the processing of the films. Further optimization of the attenuation is typically effected by manipulating the thickness of the anti-reflective coating 10 and the bake process (i.e., time, temperature) to minimize the reflectivity of the anti-reflective coating 10.
Regardless, typically at least some deep ultra violet energy reflects back into the photo resist 14. One of the problems with any type of anti-reflective coating is that the light (i.e., the deep ultra violet energy) must travel through the interface between the photo resist 14 and the anti-reflective coating 10, and the interface itself is a source of reflection back into the photo resist 14. The reflected energy may be, for example, 3% or greater with some of the new SiON films which are presently being used as anti-reflective coatings. This reflected energy degrades the resist image by creating constructive and destructive properties as the reflected energy passes back through the resist film stack in an unpredictable manner.
A general object of an embodiment of the present invention is to provide a method to improve the resolution of a photolithography system by using one or more coupling layers between a photo resist and an anti-reflective coating.
Another object of an embodiment of the present invention is to provide a method of photolithography wherein the energy which is reflected back into the photo resist is minimized.
Still another object of an embodiment of the present invention is to provide a method of photolithography which uses one or more coupling layers between a photo resist and an anti-reflective coating in order to compensate for a mis-match in indexes of reflection between the photo resist and anti-reflective coating.
Briefly, and in accordance with at least one of the foregoing objects, an embodiment of the present invention provides a method of photolithography which includes steps of providing a wafer, depositing a film on the wafer, applying an anti-reflective coating to the substrate, providing a photo resist, and providing one or more coupling layers between the anti-reflective coating and the photo resist.
Another aspect of the present invention provides a device which is configured to be processed using photolithography. The device includes a wafer, a substrate, a photo resist, an anti-reflective coating between the photo resist and the substrate, and one or more coupling layers between the photo resist and the substrate.